Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
- The entire Abbott family knowing ASL due to Regan's deafness is what allowed them to survive the initial chaos as they had a way to effectively communicate non-verbally when it became known the monsters hunted by sound. This is confirmed in the sequel.
- On a meta level, the only way to survive the film is to not make any noise... which includes talking to the person sitting next to you, letting your cell phone ring, munching very loudly on popcorn, or slurping on soda. A number
of film journalists have noted that this movie managed the impossible: it made audiences shut up during a PG-13 horror movie. - Why is Regan so upset when Lee wants her to try wearing a cochlear implant? In the first scene, she seems happy wearing it, even though it doesn't work. She's also seen checking on Beau and Marcus in that scene; she leaves the safe path when she sees Marcus's flashlight and jumps into the silo when Marcus is slipping under, nearly dying herself. That moment with Lee handing her the Leatherman tool in that first scene showed them to be close, showed her to be trying to take after him, and just like him she has shades of protective sibling to her. Regan was the closest to Beau. She doesn't just blame herself for the rocket, she blames herself because if the implant were working that day, she could have saved him.
- The monsters, according to notes the father takes, don't eat their prey. This seems strange, as they're on a constant rampage killing everything they can hear, but chances are with an evolutionary history unrelated to Earthly life, the aliens' biochemistry and terrestrial biochemistry aren't compatible. They want to eat, but nothing they find is edible. So, they keep hunting and killing, hoping desperately that the next kill is food they can eat.
- One of the aliens finds itself in a flooded room and submerges totally underwater. Why would it do this? Because sound travels farther in water than in air.
- Possibly also because it allows them to move more stealthily, like a crocodile.
- In the town's abandoned grocery store, the shelves looked like they have been long picked clean of food, with the exception of foods in crinkly packaging, like potato chips.
- Similarly, the pharmacy is well stocked, because most of the pills are in bottles that make noise when shaked. Only the most desperate would raid the pharmacy to get medicine, which the Abbots do, but carefully, and only what they absolutely need.
- In the scene where they're playing a game of monopoly, the dice are thrown very meticulously, not on the board, but on the rug next to the board. Of course they would have become accustomed to doing that. Dropping the dice on the rug negates any sound they would have made, as opposed to the usual noisy clatter of dropping a pair of dice onto a hard surface. As well as using, not the usual metal game pieces which would clack every time you set them down, but makeshift game pieces made of a softer material. The lengths they went to in order to ensure as little sound as possible, even for a simple game, is simply astounding.
- The father's board in the bunker containing information about the aliens says that there are three of them confirmed to be in the area. When the mother manages to kill one alien in the climax, the Bolivian Army Ending shows the other two aliens in the area closing in on the family's location after being attracted by the gunshot that killed the first alien.
- Why does everyone seem so darn clumsy in this movie? Horror movie rules? Nope. Consider what happens when, say, you're walking through your own house in the dead of night while trying not to wake anyone else. If you know someone is a light sleeper, or are just that afraid of them being woken, every sound you make will seem louder to you. Every creaky floorboard, every accidentally bumped piece of furniture. Now multiply the danger by monster and make the consequence for noise be death. You're no doubt going to be made extra aware of every little sound you make, even moreso if something is always listening and waiting to kill whatever makes a sound. It's not that the people are so much clumsier. It's just that you're more aware of all the sounds they make.
- Additionally, bumping into things, tripping, and accidentally hurting yourself are common facts of life. You bump into something, say 'ow', and carry on with your life. There's just no consequence. Humans are naturally clumsy creatures. There's just not normally not a fatal consequence to clumsiness.
- Why doesn't Lee take Regan with him on errands, even though she volunteers and Marcus clearly wants to stay home? While she clearly thinks it's because her father blames her, it can be deduced that he's probably worried about her making a noise, or being near a noisy animal, and not being able to realize it.
- One can sit for hours and think about all the ways that life would be nearly impossible without the ability to make noise. Snore in your sleep? Get murdered in your bed. Catch a cold? A single cough or sneeze could be a death sentence.
- The future of a newborn within the world is just a litany of horror. Putting an infant in a sound-proof box is one temporary solution to saving its life, but how do you raise a young child to understand that it can't make sound? How do you teach a toddler not to laugh or cry? How long would the child need to be raised in a soundproof room before it could be trusted to leave and experience the outside world? What kind of psychological toll would it take on the human mind being raised in that way?
- Much of Earth's ecosystem will soon be seriously thrown off-balance due to animals not being able to figure out that they need to be silent. With humanity nearly hunted into extinction with that knowledge, most species of animals, including pets and livestock are going to be slaughtered into oblivion.
- A note on the father's board indicates that the monsters don't eat their prey. They may not be able to digest terrestrial life, but we know that they can survive for unknown but extremely long amounts of time without food (Word of God indicates that they survived on asteroids after their home planet was destroyed). They're going to be on the brink of starvation, but not to the point of dying, though they will continue to get hungrier and hungrier, attacking and killing more and more in desperation to find something they can eat.
- The implied Heroic Sacrifice of the final newspaper announcing that the aliens hunt by sound. Everyone who printed that paper in noisy printing presses and distributed it by noisy cargo truck must have known that they were drawing the aliens to them like beacons.
- We only see eight human beings on screen during the entire film, one of whom is already dead. It's not certain if there are even any left after the 472 days.
- According to John Krasinski, the monsters are aliens that survived the destruction of their homeworld and, thanks to their thick armor, survived in asteroid chucks of it that drifted through space until they reached earth. Considering how long it would realistically take for asteroids from even the nearest stars to reach earth, that means these creatures can survive for millions or potentially billions of years even in the vacuum of space. Not only does this mean it's impossible to wait them out, but it gives some potential ideas for their numbers. Best case scenario, there's only a small few that survived and they were been dormant during all that time until they made it to earth. Worst case, that's tens of thousands of generations surviving and reproducing in those asteroids without the need for food, water, air, or even gravity, just waiting until they made it to a new planet...
- There must be no pet dogs left alive. Even the best trained dog can't make no noise, and most of them would immediately bark at any nearby creature. Anyone with a pet dog at the time of the invasion would have no real choice but to abandon it if it even survived the initial assault. This became an Ascended Fridge Horror in the sequel, and thankfully, viewers are barred from seeing it happen besides the dogs barking...
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